The disclosures of Japanese Patent Application Nos. HEI 10-57985 filed on Mar. 5, 1999 and HEI 10-62092 filed on Mar. 9, 1999 including the specifications, drawings and abstracts are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a control device and a control method for controlling a base injection amount of fuel in a vehicle in which a direct fuel injection type engine is installed.
2. Description of the Related Art
Many vehicles in which a direct fuel injection type engine is installed have an air flow meter and an intake pipe negative pressure sensor disposed in an intake pipe, with a view to precisely determining an air-fuel ratio of mixture gas. In these vehicles, an amount of intake air, which changes in accordance with the opening and closing of a throttle valve operated through an accelerator pedal, is calculated based on an amount of air flow detected by the air flow meter and a negative pressure detected by the intake pipe negative pressure sensor, and the base injection amount of fuel is controlled based on the calculated amount of intake air of the engine such that an optimal air-fuel ratio is achieved.
For such engines, there has been proposed a control device designed to cause different types of combustion by changing the timing for fuel injection in a combustion cycle. For example, during low-load operation (at the time of a low rotational speed), mixture gas of a high fuel concentration is biased toward a zone in the vicinity of an ignition plug of the engine, and a first control wherein fuel injection is carried out in the latter half of the compression stroke of the engine is performed so as to cause so-called stratified combustion. During high-load operation (at the time of a high rotational speed), mixture gas is evenly distributed in the combustion chamber, and a second control wherein fuel injection is carried out in the intake stroke of the engine is performed so as to cause so-called homogeneous combustion.
By the way, it is known in a vehicle provided with a continuously variable transmission that if the continuously variable transmission has been operated toward a lower speed based on a requirement for sudden acceleration resulting from depression of an accelerator pedal, the vehicle body oscillates longitudinally at the time of termination of the speed-change operation. This oscillation is called bucking or transient surge. That is, if the continuously variable transmission is operated toward a lower speed in response to a requirement for sudden acceleration, the rotational speed of rotating bodies relating to transmission of motive power changes, and an inertia torque corresponding to an amount of change in rotational speed (angular acceleration) and an inertia moment is generated. When the rotational speed of those rotating bodies settles down to a target rotational speed after termination of a speed-change operation, the inertia torque is released. As a result, the driving torque temporarily increases due to the inertia torque, and the vehicle oscillates longitudinally against the oscillating elasticity of a power transmission system.
For example, in order to damp transient surges of this kind, the present applicant has proposed a device disclosed in Japanese Patent Application No. HEI 11-5460. In this device, based on an output torque of the engine and a speed-change ratio, a half cycle of transient surge oscillation, which is expected in terminating a speed-change operation, is calculated. At a predetermined time determined on the basis of a point of time prior to a point of time of generation of the expected transient surge oscillation by a half cycle, both the output torque of the engine and the speed-change ratio of the CVT are controlled. Thereby oscillation of an opposite phase is generated to counterbalance the transient surge oscillation of the vehicle body. In this manner, the transient surge oscillation is damped. Hereinafter, the control for thus damping longitudinal oscillation of the vehicle by controlling at least one of the engine and the continuously variable transmission will be referred to as transient surge damping control. The transient surge damping control is particularly effective in a direct fuel injection type engine with a good operational response performance.
On the other hand, as for oscillation of the vehicle, there is a device designed to perform so-called smoothing control wherein the output torque of the engine is gradually reduced by outputting a decreasing base injection amount step by step so as to attenuate a shock at the time of deceleration such as sudden braking.
However, in the case where the transient surge damping control at the time of sudden acceleration and the smoothing control at the time of deceleration are applied to a vehicular control device designed to selectively perform the first control and the second control as described above, if a transition from the second control to the first control or vice versa is made during performance of the transient damping control or the smoothing control, because of a discrepancy in control amount between the first control and the second control, there occurs a shock caused by abrupt fluctuations of torque. As a result, there arises a problem of an inability to effectively perform the transient surge damping control and the smoothing control.
Because the transient surge damping control is intended to counterbalance transient surge oscillation, control amounts need to be outputted at extremely precise timings. However, since the change in amount of intake air is temporally offset from the change in output torque of the engine, the transient surge damping control based on an amount of intake air of the engine makes it difficult to output control amounts at precise timings.
It is an object of the present invention to effectively perform transient surge damping control and smoothing control in a control device and a control method for a vehicle designed to selectively perform the first control and the second control.
According to a first aspect of the present invention, there is provided a control device for a vehicle provided with an engine and a continuously variable transmission, comprising first control means for carrying out fuel injection in an intake stroke of the engine so as to evenly distribute mixture gas into a combustion chamber of the engine, second control means for carrying out fuel injection in a compression stroke of the engine so as to bias mixture gas toward a zone close to an ignition plug of the engine, transient surge damping control means for damping longitudinal oscillation of the vehicle by controlling at least one of the engine and the continuously variable transmission, and selection means for selecting either control through the first control means or control through the second control means in accordance with a loaded condition of the engine and for prohibiting a transition from the second control to the first control if the transient surge damping control is being performed when a loaded condition of the engine becomes suited for a transition to the first control during performance of the second control.
In the first aspect of the present invention, during performance of the second control wherein fuel injection is carried out in an intake stroke of the engine so as to evenly distribute mixture gas into the combustion chamber of the engine, even if the engine has reached a loaded condition suited for a transition to the first control wherein fuel injection is carried out in a compression stroke of the engine so as to bias mixture gas toward a zone in the vicinity of the ignition plug, as long as the transient surge damping control is being performed for the engine or the continuously variable transmission, the transition to the first control is not made. The transition to the first control is made on condition that the transient surge damping control has been terminated. In this manner, according to the first aspect of the present invention, the transition from the second control to the first control is made after termination of the transient surge damping control. Therefore, there is no possibility of a shock occurring due to such transition being made during performance of the transient surge damping control. Further, in the case where the transient surge damping control is performed based on an opening degree of the throttle valve, the response performance is improved in comparison with the case where the transient surge damping control is performed based on an amount of intake air. Thus, control amounts can be outputted at extremely precise timings. Accordingly, the first aspect of the present invention makes it possible to effectively perform the transient surge damping control.
According to a second aspect of the present invention, there is provided a control device for a vehicle provided with an engine and a continuously variable transmission, comprising first control means for carrying out fuel injection in an intake stroke of the engine so as to evenly distribute mixture gas into a combustion chamber of the engine, second control means for carrying out fuel injection in a compression stroke of the engine so as to bias mixture gas toward a zone close to an ignition plug of the engine, smoothing control means for gradually reducing an output torque of the engine during deceleration of the vehicle, and selection means for selecting either control through the first control means or control through the second control means in accordance with a load condition of the engine and for prohibiting a transition from the first control to the second control if the smoothing control is being performed when a loaded condition of the engine becomes suited for a transition to the second control during performance of the first control.
In the second aspect of the present invention, during performance of the first control wherein fuel injection is carried out in a compression stroke of the engine so as to bias mixture gas toward a zone in the vicinity of the ignition plug, even if the engine has reached a load condition suited for a transition to the second control wherein fuel injection is carried out in an intake stroke of the engine so as to evenly distribute mixture gas into the combustion chamber of the engine, as long as the smoothing control for gradually reducing the output torque of the engine at the time of deceleration of the vehicle is being performed, the transition to the second control is not made. The transition to the second control is made on condition that the smoothing control has been terminated. In this manner, according to the second aspect of the present invention, the transition from the first control to the second control is made after termination of the smoothing control. Therefore, there is no possibility of a shock occurring due to such transition being made during performance of the smoothing control. Thus, the smoothing control can be performed effectively.
According to a third aspect of the present invention, there is provided a control device for a vehicle provided with an engine and a continuously variable transmission, comprising first control means for carrying out fuel injection in an intake stroke of the engine so as to evenly distribute mixture gas into a combustion chamber of the engine, second control means for carrying out fuel injection in a compression stroke of the engine so as to bias mixture gas toward a zone close to an ignition plug of the engine, selection means for switching the first control and the second control from one to the other in accordance with a loaded condition of the engine and performing the selected control, third control means for performing, for a predetermined length of time, control wherein fuel injection is carried out in both a compression stroke and an intake stroke of the engine, when the selection means switches the first control and the second control from one to the other, transient surge damping control means for damping longitudinal oscillation of the vehicle by controlling at least one of the engine and the continuously variable transmission, and prohibition means for prohibiting performance of the third control when the transient surge damping control is being performed.
In the third aspect of the present invention, in a normal running state where the transient surge damping control is not being performed, when switching the first control wherein fuel injection is carried out in a compression stroke of the engine so as to bias mixture gas toward a zone in the vicinity of the ignition plug and the second control wherein fuel injection is carried out in an intake stroke of the engine so as to evenly distribute mixture gas into the combustion chamber of the engine, from one to the other, the third control wherein fuel injection is carried out in both a compression stroke and an intake stroke of the engine is performed for a predetermined length of time. While the transient surge damping control for damping longitudinal oscillation of the vehicle by controlling the engine or the continuously variable transmission is being performed, the second control is not performed. Therefore, according to the third aspect of the present invention, even if the fuel injection amount for controlling the output torque of the engine has increased from a zone suited for stratified combustion to a zone suited for homogeneous combustion while the transient surge damping control is being performed, the concentration of fuel in the vicinity of the ignition plug does not become excessively high or excessively low. Thus, the transient surge damping control can be performed effectively.